Growing environmental awareness has led to recent improvement in legal systems for controlling the fuel volatility. Especially in the automotive industry, the fuel volatility control is seriously demanded particularly in the United States. This demand has raised needs for materials having excellent fuel-barrier properties.
In particular, common rubber hoses for fuel transfer are laminate hoses (rubber is used except for a barrier layer) having a barrier layer made of a fluororesin for enhancing the fuel permeability resistance. Recent strong demand for reduction in environmental loads has raised needs for lower fuel permeability of the barrier layer. To achieve this, increase in the barrier layer thickness and use of a perhalogen fluororesin that has the lowest permeability among fluororesins have been considered as means for ensuring lower permeability. However, increase in the barrier layer (fluororesin) thickness leads to increase in the hose weight and is also disadvantageous from the standpoint of energy conservation. Additionally, bendability (flexibility) of the hose is lowered, which is disadvantageous in terms of handleability (assembling property).
In the case that a perhalogen fluororesin is used in a barrier layer, the barrier layer is not easily adhered with a rubber of inner and outer layers. This requires an additional step such as a step of surface treatment of the resin for improving the adhesiveness and a step of winding a film or tape around the layer. Such a complicated process significantly lowers the productivity and also greatly increases the cost, which are practically disadvantageous.
Patent Document 1, for example, discloses use of epoxidized rubber or a blended material containing epoxidized rubber and another rubber in a rubber layer, as a method for enhancing the adhesion between a fluororesin layer and a rubber layer. Further, as disclosed in Patent Document 2, another known method for improving the adhesion is using a thermoplastic fluororesin having a reactive functional group such as a carbonyl group as a fluororesin and adding a polyfunctional compound such as triallyl isocyanurate to at least one of the thermoplactic fluororesin and a rubber layer for direct adhesion between the fluororesin and rubber.
Patent Document 3 discloses a fuel hose having a layered structure in which a diene rubber layer and a vinylidene fluoride copolymer (THV) layer are adjacent to each other. The diene rubber layer comprises a diene rubber such as NBR added with a sulfur vulcanizing agent, at least one of a metal calbamate and a thiazole metal salt, and magnesium oxide, along with a DBU salt and the like.
As disclosed in Patent Documents 4 and 5, adhesiveness of a curable elastomeric compound to a fluoropolymer layer may be enhanced by using a fluoropolymer having at least one monomer unit containing a plurality of hydrogen atoms or a fluoropolymer essentially containing a vinilydene fluoride unit and blending a dehydrofluorinating composition therein.    [Patent Document 1] JP-A 7-266501    [Patent Document 2] JP-A 2005-22403    [Patent Document 3] JP-A 2007-261079    [Patent Document 4] JP-T 2001-527104    [Patent Document 5] JP-T 2001-526972